Sonia D. Hudson Charles A. Sims Asli Z. Odabasi Thomas A. Colquhoun Derek J. Snyder Jennifer J. Stamps Shawn C. Dotson Lorenzo Puentes and Linda M. Bartoshuk
Taste and flavor (retronasal olfaction) interact in the brain. The rules of that interaction are not well understood. This study uses 2 taste modifiers that alter sweet to examine the effects on flavors. Subjects used the Global Sensory Intensity Scale to assess the aroma, sweetness, sourness, and flavor of 10 foods. As previous work had shown, miracle fruit added sweetness to acids, which secondarily reduced sourness (mixture suppression) and Gymnema sylvestre reduced sweetness in sweet foods as well as the sweetness induced by miracle fruit. In this study, multiple regression showed that both sweet and sour contribute to flavor. Gymnema sylvestre reduced the perceived sweet of predominantly sweet foods (chocolate and maple syrup) as expected; reducing the sweet, reduced the flavor. The effects of miracle fruit were complicated by its dual action: intensification of sweet and reduction of sour. Predominantly sour foods (vinegar, lemon, mustard, pickle) were sweetened by miracle fruit but any flavor enhancement associated with the added sweet appears to have been countered by the flavor reduction associated with reduced sourness. Moderately sour foods that are also sweet (tomatoes, strawberries) were sweetened by miracle fruit and thus flavor was enhanced; flavor loss through sour reduction was apparently not sufficient to counter the flavor enhancement due to increased sweet so the net result was that tomato and strawberry flavors were enhanced.
Eating foods stimulates complex sensations. The anatomy is clear. Taste stimuli (nonvolatiles) excite cranial nerves (CNs) VII, IX, and X. Olfactory stimuli (volatiles) excite CN I. Touch, irritation/pain, and temperature excite CNs V and IX. Chemosensory terminology is less clear. In everyday language, the terms “taste” and “flavor” are used as synonyms to refer to the complex of sensations resulting from chewing and swallowing food. However, these terms are also used to refer to specific sensations within this complex. Perhaps the greatest confusion arises because olfactory stimuli can be perceived in 2 ways. Sniffing brings volatiles from the environment through the nostrils and up into the nose to binding sites on the olfactory receptors in the olfactory mucosa; this is called “orthonasal olfaction” (commonly called “smell”). When foods that emit volatiles are chewed and swallowed, the volatiles are forced up behind the palate
and into the nose from the rear where they ultimately contact the binding sites; this is called “retronasal olfaction.”
Modern use of “taste” and “flavor” The word “taste” can be used as a verb: “I taste food.” The word “flavor” can also be used as a verb, “I flavor food.” However, when flavor is used as a verb it refers to adding a flavoring ingredient to food, not perceiving the flavor of the food. English lacks a verb that describes perceiving retronasal olfaction. Thus the sentence “I taste food” can have dual meaning. “Taste” can refer to a sensation arising from taste buds (e.g., I taste sweet) or it can refer to retronasal olfaction (e.g., I taste cinnamon).
In this article, when the word “flavor” is used, it is intended to refer to the sensations evoked by volatiles perceived retronasally. Of special interest for this study, retronasal olfaction and taste can alter one another, presumably in the brain. The rules governing these interactions are still not well understood; some examples are discussed in the following sections.
In our studies, we measured chemical constituents (e.g., sugar content as well as the content of various volatiles) and asked subjects to rate sensory attributes of the fruit including sweet, and fruit flavor. Multiple regression analyses were performed initially with perceived sweet as the dependent variable with sugar content and perceived fruit flavor as the independent variables. These analyses showed significant contributions of perceived flavor to the perceived sweet that were independent of the contributions of sugar. Multiple regression analyses with perceived sweet as the dependent variable but with sugar content and a given volatile as independent variables allowed us to determine which of the volatiles that made up the flavor of the fruit were responsible for the contribution to perceived sweet.
The effects of both miracle fruit and G. sylvestre are temporary—only lasting between 30 min and 1 h. The emerging information about the interactions between taste and flavor (noted earlier) suggests that taste modifiers should affect flavors as well as taste.
Materials and Methods
This study was conducted according to the principles of the 1975 Declaration of Helsinki and Good Clinical Practice guidelines and was approved by the University of Florida Institutional Review Board. Written and verbal informed consent was obtained from each participant. One hundred panelists (18–55 years) were recruited from students and staff of the University of Florida. Subjects were excluded if they were vegetarians (the foods included chicken sausage), had allergies to any of the foods to be tested, or disliked any of the foods (and so were reluctant to taste them). All panelists participated in a training session before the tasting experiments to familiarize themselves with the Global Sensory Intensity Scale (GSIS). The training and tasting sessions took place in the University of Florida Food Science and Human Nutrition Department sensory laboratory. This facility contains 10 individual booths equipped with computers running Compusense.
Panelists used the GSIS to rate the intensities of 10 food samples. Panelists sniffed the food samples to rate aroma and placed the samples in the mouth, chewed, and swallowed to rate sweetness, sourness, and the flavor of each food. The GSIS is the result of methodological research aimed at providing valid comparisons between groups.
Subsequent research suggested removing “imaginable” and the intermediate descriptors. The GSIS runs from 0 (no sensation) to 100 (strongest sensation of any kind ever experienced) with no intermediate intensity descriptors. To provide valid comparisons of taste intensities, the top of the scale (strongest sensation of any kind ever experienced) must be independent of taste. Panelists rated the intensities of aroma, sweetness, sourness, and flavor of the 10 food samples before and after exposure of the tongue to the taste modifiers under investigation.
Ten food samples were selected to represent a range of foods containing varying levels of sweet and/or sour tastes. Foods were predominantly sour (apple cider vinegar, lemons, French’s yellow mustard, Mt. Olive dill pickle chips), predominantly sweet (Hershey’s dark chocolate Kisses, Aunt Jemima original maple syrup), or both sour and sweet (tomatoes and strawberries). Control foods had very little sour or sweet taste (Armour chicken Vienna sausages and Planters unsalted peanuts). Unsalted crackers and water were provided at all times; subjects were instructed to cleanse their palate before and after each sample.
Commercially available freeze-dried miracle fruit tablets, “mberry,” were obtained from My M Fruit, LLC. Each tablet was stated to be equivalent to approximately 1 miracle fruit berry. Panelists were instructed to let the tablet dissolve in the mouth, moving it around
without chewing. In approximately 5 min, panelists began the food sampling and rating the 10 foods.
Gymnema sylvestre tea
Gymnema sylvestre leaves (Penn Herb Company, Ltd) were brewed as a tea beverage shown to reduce perceived sweetness according to the recipe originally developed by Meiselman: 1500 mL hot water and 100 g tea leaves stirred for 1 h at 95 °C . The tea was stored in a refrigerator and warmed to room temperature before using. Subjects held 10 mL in the mouth for 30 sand then expectorated. Panelists rated the foods after exposure of the tongue to the G. sylvestre tea.
Note that the experiments were performed on separate days in the order indicated under “Panelists”; however, the results are presented ordering the modifiers conceptually: miracle fruit, G. sylvestre, and miracle fruit followed by G. sylvestre. As noted earlier, the foods were selected based on the magnitudes of the sour and sweet sensations (before modification) and they were organized into those groups. The leftmost columns show the results for miracle fruit. Ratings before and after miracle fruit were compared using paired t-tests with Bonferroni corrections. That is, given 40 observations (10 foods, 4 qualities) the individual P value for a t-test had to be less than 0.00125 to be considered significant at P < 0.05 (“–” for a decrease or “+” for an increase). For G. sylvestre with similar Bonferroni corrections. The right-most columns show the results for the experiment that tested first miracle fruit and then G. sylvestre. The “aft MF” column compares ratings before to those after miracle fruit. The “aft MF and GS” column compares ratings after miracle fruit to those after both modifiers. t-Tests comparing ratings before either modifier to ratings after both modifiers are described in the text. Bonferroni corrections: given 10 foods, 4 qualities, and 3 comparisons, the individual P values for t-tests had to be less than 0.00042 to be considered significant at P < 0.05.
Analysis by food groupings
Predominantly sour foods (vinegar, lemon, mustard, pickle) After miracle fruit these foods tasted sweeter and less sour. Flavor was not intensified and, in fact, was significantly reduced for vinegar and lemon.
Gymnema sylvestre had relatively little effect on these foods because they produce little sweetness; however, after G. sylvestre the small amount of sweetness present was reduced. Aroma was essentially unchanged except that the aroma of vinegar was slightly reduced.
Sour and sweet foods (strawberry and tomato)
After miracle fruit, these foods tasted sweeter and less sour just as for predominantly sour foods. However, for these sour and sweet foods, flavor was intensified after miracle fruit. After G. sylvestre, sweetness and flavor were reduced. In the experiment with both modifiers, the effects after miracle fruit were the same as when miracle fruit was the only modifier presented, as expected; foods were sweeter and less sour; flavor was
Intensified. After G. sylvestre and miracle fruit, sweetness and flavor were reduced and sourness was intensified. Comparisons of ratings before either modifier with those after
both modifiers showed that sweetness ratings were reduced to values below those before either modifier.
Predominantly sweet foods (syrup and chocolate)
Miracle fruit had no effects on these foods.
After G. sylvestre, sweetness and flavor were reduced. In the experiment with both modifiers, the effects after miracle fruit were the same as when miracle fruit was the only modifier presented, as expected; miracle fruit had no effect. After G. sylvestre and miracle fruit, the effects were also the same as for G. sylvestre alone; sweetness and flavor were reduced. Comparisons of ratings before either modifier with those after both modifiers showed sweetness and flavor ratings were significantly below the premodifier ratings.
Control foods: little sour or sweet (chicken sausage and peanuts)
For the most part, these control foods showed only small changes with either modifier; however, some of them achieved statistical significance. In general, these small changes are similar to the changes noted earlier: sweetness was intensified after miracle fruit; sweetness and flavor were reduced after G. sylvestre.
Analysis of contributions of sourness and sweetness to flavor
In this study, we used multiple regression (SPSS; SPSS Inc.) to study associations between sourness, sweetness, and food flavor; data used came from the first occasion on which subjects tasted the foods (“before” condition for the experiment using both modifiers). Each of the foods that were either predominantly sour or both sour and sweet (vinegar, lemons, mustard, pickles, strawberries, and tomatoes) was analyzed individually with the perceived food flavor as the dependent variable and the perceived sweetness and perceived sourness as the independent variables. Bonferroni corrections (6 foods with 2 taste qualities for each) showed that for all 6 foods, sourness was a significant contributor to flavor at P < 0.01. Sweetness was also a significant contributor to flavor for strawberry (P < 0.01) and tomato (P = 0.01).
Effects of miracle fruit and G. sylvestre on the tastes of the foods
After miracle fruit, sweetness was intensified in predominantly sour foods as well as sour and sweet foods. The chicken sausage was the only additional food to show a significant increase in sweetness (albeit a small increase); this was presumably due to a small amount of acid in the sausage. This corroborates (using foods) the results of previous studies using pure acids. After G. sylvestre, all of the sweet tastes (with the exception of a small amount of sweetness reported for the chicken sausage) were reduced. This corroborates (using foods) the results of previous studies using a variety of sweeteners.
In the experiment using both modifiers, not surprisingly for the sour and sweet foods (strawberry and tomato), after G. sylvestre, the original sweetness and the sweetness intensification following miracle fruit was reduced. We previously showed that after miracle fruit, pure acids tasted sweet as well as less sour. After subsequent G. sylvestre, that sweet ness was abolished and sourness returned to near original values.
The results of this study show similar results when sweet and sour foods were the stimuli.
Effects of miracle fruit and G. sylvestre on the flavors of the foods
This study confirms previous studies showing that sweet and sour tastes can intensify flavor. Thus, we predicted that the changes in sweetness and sourness induced by modifiers should alter flavors in foods. Elevations in sweet should intensify flavor; reductions in sweet or sour should reduce flavor. Sweet was reduced by G. sylvestre in the sweet foods and flavor was reduced in all of the cases where sweet reduction was
substantial, as predicted. The only failures of flavor reduction occurred for the small amount of sweetness reduction in the predominantly sour foods. Sweet was enhanced by miracle fruit in the sour foods. However, flavor was only enhanced in foods that were sour and sweet; flavor was not enhanced in predominantly sour foods. When miracle fruit is used with acidic foods and drinks, “underlying layers of flavor become more perceptible”. We suggest that this may be due to intensification of flavor produced by the intensification of sweetness associated with miracle fruit.
A few studies have shown that miracle fruit makes food more palatable to patients having cancer. One of the comments made by a patient having cancer was that food had “more flavor than usual.” Note that these comments suggest that part of the success of miracle fruit in enhancing eating is an intensification of flavor rather than simply the addition of a sweet taste. The results of this study support such anecdotes and may help select the foods where enhancement of flavor will be most likely to occur.
Full journal research available here.